texas lm358p dual op amp

I have a wine cooler that I want to turn into a incubator. Normally I would built the controls from scratch but on this model if I can understand the controls there may be a simple fix.

boring info:

the cooler is 2 x peltier based it has 2 x 12v power supplys
one control board is basically a mosfet the other board and is hard wire slaved to the main board

on the main board with the dual op amp you have a mosfet that is being supplied by transistor that is connected with a few other compents to the dual op amp

there was a thermostat type device (may be just a pot) that you could select colder-hotter.

there is a temp sensors (2 wire)

the chip is 8 pin it looks like pins 1-2-3 are not connected (not soldered to the board)

on the print I think that means that

pin1 - 1 output
pin2 - 1 input -
pin3 - 1 input +

are not being used

so im guessing its being used as a single op amp really

pot I think following the traces is pin 5 via a reisitor listed as 2 input +
temp uses a few compents and seems to end at pin 6 listed as 2 input -

pin 7 is what interests me. Can I remove just the chip and connect the a arduino uno to control the mosfets / peltiers just by connecting the arduino to what use to be the 2 ouput pin on the chip and connecting the negatives between the power supply and the arduino

what kind of single would the op amp have been putting out to the mosfets (pwm or simple on off)

Any help or advice would be welcome (still trying to find a basic idiots guide to op amps)

maybe im thinking about this wrong but if I connect a resistor across where the temp sensor use to be connected then connect the arduino to the input + as long as the arduino output is higher voltage that the input - pin the amp should output a positive signal driving the mosfets (have to check with a meter to make sure it not working backwards)

what kind of single would the op amp have been putting out to the mosfets (pwm or simple on off)

The best approach is to carefully measure voltages while the original board is running. Check the op amp output voltage with respect to the board ground in the heater/cooler on and off states.

It will either be low or high or if pwm (unlikely) then somewhere in between. If high and significantly greater than 5 V (like 10-12) then the Arduino probably cannot be used to control those MOSFETs directly, as they are not logic level.

op amp output voltage is 7v but after further testing its looks like im going to have to build my own board as power on the output shuts the peltier down where I want it to fail the other way for safety.

I really do appreciate you taking your time to reply.

Hi,
How complicated is the PCB, can you reverse engineer it?
Draw a schematic, as by the looks of it, all components are marked.

Tom.... :slight_smile: